oa Biomarker Study of Paleogene Sediments, IODP Site U1435, Northern South China Sea: Organic Matter Inputs and Palaeoenvironment Reconstruction

This study analyses the biomarkers in Paleogene sediments from IODP U1435 site to investigate organic matter input and paleoenvironmental changes during the Paleogene. The average carbon preference index (CPI22-32) for the Oligocene is higher than the pre-Oligocene, with significantly increased terrigenous organic matter (OM) input during the late part of the pre-Oligocene. The Pr/Ph ratios and the terrestrial/aquatic ratio of the pre-Oligocene samples at depths >140 m CSF-B are significantly lower than those of the late part of the pre-Oligocene and the Oligocene, indicating an up-core change from an anoxic to oxic depositional environment and an increase in terrigenous OM inputs. The hopanoid distributions of the Oligocene samples are composed of C27-C30 neohop-13(18)-enes, C27-C31 hop-17(21)-enes, C27-C35 aß hopanes, C27-C32 ßa hopanes, C30-C33 ßß hopanes, oleanane, and gammacerane. In contrast, the hopanoid distributions of the pre-Oligocene samples lack C27-C29 neohop-13(18)-enes and C27-C31 hop-17(21)-enes. In the Oligocene samples the higher abundance of C29 steranes and sterenes, especially the ßaa and aaa20R isomers, compared to C27 steranes and sterenes, supports the strong terrigenous OM input during the Oligocene. In contrast, the pre-Oligocene sample has more C27 than C29 steranes and sterenes, indicating OM inputs dominated by algae.